In the field of hard disk storage systems, continuous improvements have been made in increasing the areal density (i.e., the number of stored bits per unit of surface area) of the magnetic recording disks. As is well known, decreasing the fly height of the read/write head, for example, results in reduced PW50 (the pulse width where the read head output amplitude, in response to an isolated transition, is 50% of the peak value) that allows for greater recording density. Bringing the head closer to the media has been a key area of effort in increasing recording densities.
In current disk drive systems that employ flying heads, there is a protective film of air between the slider and the disk, where no contact is intended to occur during head read/write operations. The read/write head element is typically a part of or coupled to a larger body that flies over the disk and is typically referred to as a “slider.” The slider has a lower surface referred to as an air bearing surface (ABS). The ABS generally generates a positive air pressure. In addition, there is often a cavity or similar structure that creates a sub-ambient pressure to counterbalance the positive pressure to some extent. The slider body is attached to a suspension via a head gimbal assembly that biases the slider body towards the disk. The net effect of the ABS and the suspension is to cause the slider, and coupled head, to fly at the desired height when the disk is at full speed. The net effect also causes the slider to be in contact with the disk surface, when the disk is at rest, in contact-start-stop (CSS) disk drive systems. This contact between the slider and the disk occurs in an area when the drive is turned on and off, and is known as a CSS zone. Another type of disk drive system, referred to as load/unload disk drive system, parks the slider (more particularly a suspension arm on which the slider is secured) on a ramp, not the disk surface, when the drive is turned off.
In both types of disk drive systems, the head is idle and flies over a data zone while the disk is rotating awaiting instruction during a significant portion of the time in operation. As the flying height of the read/write head is reduced in the effort to increase recording densities, the frequency and likelihood of intermittent contact with the disk increases during drive operations. Such intermittent contact may cause the head to fly unstably and result in erroneous read back of data. In the worst-case scenario, if the impact of a hit is too severe, it may cause a head crash and damage the head and/or disk. Since the disk rotates very fast during normal operation of the drive, a concern is that the head should not undesirably contact the disk.
The ever increasing areal density demands are driving some advanced designs of disk drive systems to utilize contact-type or near contact type magnetic head technology, where the head is in direct contact with the disk when in operation. One problem of utilizing this head technology is that the continuous wear from the head will degrade the disk's surface by the slow displacement of lube and eventual wear of the protective carbon coating from the disk's surface. Such wear will eventually lead to catastrophic failure and loss of data. Another problem with contact or near contact recording head technology is head degradation, by way of flash temperatures (e.g., momentary, ultra-high temperatures from friction between head and disk), that may render the magnetic head transducer sensitivity unusable by the switching of the magnetic pin layer fields. Furthermore, the head and magnetic disk interface will be subject to higher sensitivity to both particulate and outgassing contamination that will result in heightened risks for thermal asperity or high fly read or write errors.
Furthermore, reducing the fly height of a head in the data zone increases the possibility of the slider inadvertently contacting a landing zone feature (e.g., a CSS zone laser bump) or a disk surface during load/unload operations. For example, in conventional CSS drives, the height of laser bumps on a CSS zone is lower than the fly height of a head over a data zone to avoid contact with the laser bumps while parking. However, it becomes difficult to facilitate low bumps to avoid inadvertent contact of a slider to the side of the bumps as the fly height becomes lower unless the bump height is lowered below the fly height of the slider. However, lowering the bump height may increase the amount of stiction high enough to cause damage to the slider and/or disk surface. In addition, while powering down, the air bearing supporting the fly height of the slider is disturbed and is eventually diminished as the slider transitions away from the data zone onto a landing zone feature, increasing the possibility of inadvertent contacts.
U.S. Pat. No. 6,075,683 discloses a disk drive having a slider exhibiting two fly heights, one for writing/reading operations and a second for an idling operation. The idling operation at the second fly height is performed over the landing zone (also referred to as the idling zone) by patterning the surface of this zone with depressions. U.S. Pat. No. 6,075,683 does not overcome the inherent problem of inadvertent contact of the slider with a landing zone feature while parking.
Other conventional disk drive systems seek to lessen the adverse affects caused by the abrupt topographical changes of the disk surface when transitioning a slider from a data zone to CSS zone by including a transition zone between the data zone and the CSS zone. For example, U.S. Pat. No. 6,020,045 discloses a transition zone that has laser textured protrusions on its surface that gradually increasing in height and diameter from the data zone to the CSS zone. One problem with such a transition zone is that while it may improve the flying stability of a slider, such a transition zone does not overcome the inherent problem of inadvertent contact of the slider with a CSS zone texture while parking. Rather, the slider may inadvertently contact a protrusion in either the transition zone and/or the CSS zone. Similarly, U.S. Pat. No. 6,139,936 discloses a disk having a laser textured transition zone that does not overcome the inherent problem of inadvertent contact of the slider with a CSS zone texture while parking.